Reinforced flexible hose has long been in use in interconnecting various components of automotive air conditioning systems. Typically, these hoses have been provided with nipples or fittings which include an end portion insertable within the end of the flexible hose and a sleeve surrounding the end portion of the hose which is radially compressed or crimped to clamp the hose between the sleeve and end fitting. In order to increase the mechanical strength of the coupling as well as to increase the sealing capability thereof, a plurality of annular ribs are often provided on the fitting.
More recently, a composite type reinforced hose material has been developed which offers significant advantages over previous types of reinforced hose constructions in terms of cost, weight and lower permeability to refrigerants commonly utilized in automotive air conditioning systems, such as those comprising chlorofluorocarbons and sold under the trademarks Freon 12 and Freon 134A of E.I. DuPont. Typical refrigerants used, which are anticipated for use with the present invention as well, include those disclosed in U.S. Pat. No. 4,758,366, the teachings of which are incorporated herein by reference. This composite hose includes an inner liner fabricated from a thermoplastic material such as polytetrafluoroethylene which is characterized by its low memory characteristics and low resistance to compression setting. While this hose construction is less costly to manufacture and is lighter in weight, the presence of the liner material renders previous methods of forming fluid-tight seals with fittings relatively unacceptable due to the poor resistance to compression set of the liner material which increases the tendency for leakage to occur. Specifically, when presently known methods are employed to secure end fittings to such composite type hose, the compressive forces initially created by the crimped sleeve are relieved or reduced because the liner material tends to flow at the higher operating temperatures normally incurred. This in turn reduces the sealing effect and may result in discharge of the refrigerant as a gas. The normal operating temperatures encountered by such hose assemblies employed in automotive air conditioning generally ranges from about -20.degree. F. to about 250.degree. F. Design specifications require that such hose assemblies operate equally well at temperature ranges of -40.degree. F. to 300.degree. F. The higher temperatures are due mainly to the location of the system proximate the engine as well as from the heat generated in compressing the gas.
Thus for effective long-term sealing, one can not rely completely on a mechanical locking of the thermoplastic liner, such as shown for example in U.S. Pat. Nos. 4,106,526; 4,111,469; 4,142,554; 4,305,608; and West German Patent No. 1,164,770.
Rather, it is known to supplement the mechanical locking system as referred to above with a secondary sealing system in the form of a resilient sealing member. Examples of such a hose assembly are shown in U.S. Pat. Nos. 2,453,997; 2,797,111; 3,578,360; 3,990,729; 4,039,212; and United Kingdom Patent No. 1,083,741.
However, none of the aforementioned hose assembly sealing systems address completely and meet effectively and economically the stringent current requirements for automotive air conditioning hose assemblies which require in effect, that there be no leakage of refrigerant gas from the system for up to 12 years.